The present invention relates to the general field of heat exchangers cooled by air.
The field of application of the invention is especially though not exclusively that of condensers cooled by air in thermal power stations.
Condensers cooled by air (also called aerocondensers or ACC for <<Air-Cooled Condenser>>) are used especially in thermal power stations for production of electricity for condenser, with the steam coming from the low-pressure turbine of the plant. ACC units are advantageous alternative to condensers cooled by water. In particular, in contrast to condensers cooled by water ACCs do not release any water steam into the atmosphere, have a limited height, and do not need to be close to a cold-water source (river or canal).
Typically, an ACC comprises a plurality of ventilation modules arranged in several parallel rows, adjacent to one another and placed in the same horizontal plane to form a ventilation structure which is spaced from the ground. Each ventilation module comprises a fan for suctioning air present below the ventilation structure and blowing it vertically through heat exchange tubes in which the steam coming from the low-pressure turbine of the thermal power station circulates.
The yield from a thermal power station depends on the efficacy of the ACC heat transfer. It has been noted that ACCs are highly sensitive to external weather conditions which can considerably degrade their performance in terms of heat and vacuum transfer produced inside the condenser (also called counter-pressure turbine). This is the case for example when the surrounding temperature is high, when winds intensify or when recirculation of warm air occurs.
More precisely, it has been noted that the performance of an ACC is all the lower when the wind is strong. In fact, strong winds circulating under the ventilation structure create local drops in pressure under the fans which decrease the airflow aspired by the latter, making thermal exchange less effective. The direction of the wind also plays an important role to the extent where dominant winds can be present, as a function of the implantation site of the plant.
Also, some obstacles such as surrounding buildings, steam conduits, tanks, etc. can influence air circulation at the ACC intake and be the origin of warm-air recirculation. In particular, warm air exiting the ACC can be redirected to the ACC intake and therefore aspirated again by the fans.
To counter these problems, different panels forming a windscreen have been developed. One of the known a windscreens consists of a panel having the form of a cross which is installed under the ventilation structure to divide the aspiration space of the fans into several zones compartmentalised relative to each other. The effect of this type of windscreen which extends vertically from the ground is that the wind circulating under the ventilation structure tends to be deviated by the windscreen and directed vertically to the fans.
Although such a solution improves the efficacy of ACCs by reducing the harmful effects of strong winds, it is still not completely satisfactory.